Wednesday, 10 September 2014

CS6302 Important Two Mark Questions / CS1301 Important Two Mark Questions / CS2255-CS1301 First Unit Important Two Mark Questions / CS2255 Important Two Mark Questions with Answers / Anna University CS6302 DBMS Subject Two Mark Questions with Answers

1. Define database management system?

Database management system (DBMS) is a collection of interrelated
data and a set of programs to access those data.

7. Define the terms physical schema and logical schema.

Physical schema: The
physical schema describes the database design at the physical level, which is
the lowest level of abstraction describing how the data are actually stored. It
is about files, indices etc.

Logical schema: The
logical schema describes the database design at the logical level, which
describes what data are stored in the database and what relationship exists among
the data. This schema is used by application programmers to develop
applications.

8. What is conceptual schema?

The logical schema is sometimes called as Conceptual schema. The
Conceptual schema defines the logical structure using a data model. In the
relational model, the Conceptual schema presents data as a set of tables.

Ex. Courses(cid: string,
cname:string, credits:integer)

9. Define data model

A data model is a collection of conceptual tools for describing
data, data relationships, data semantics and consistency constraints.

10. What is storage manager?

A storage manager is a program module that provides the interface
between the low level data stored in a database and the application programs
and queries submitted to the system.

11. What are the components of storage manager?

The storage manager components include

a) Authorization and integrity manager

b) Transaction manager

c) File manager

d) Buffer manager

12. What is the purpose of storage manager?

The storage manager is responsible for the following

a) Interaction with the file manager

b) Translation of DML commands into low level file system commands

c) Storing, retrieving and updating data in the database

13. List the data structures implemented by the
storage manager.

A data dictionary is a data structure which stores meta data about
the structure of the database ie. the schema of the database. A Data Dictionary
contains the information like list of tables, list of attributes of tables,
number of records stored in a table, indices of tables etc. of any database.

It is a centralized repository of information about data such as
meaning, relationships to other data, origin, usage, and format

15. What is an entity relationship model?

The entity relationship model is a collection of basic objects
called entities and relationship among those objects. An entity is a thing or
object in the real world that is distinguishable from other objects.

16. What are attributes? Give examples.

An entity is represented by a set of attributes. Attributes are
descriptive properties possessed by each member of an entity set.

Single valued attributes: attributes
with a single value for a particular entity are called single valued
attributes. For example, Emp_Name attribute can have only one employee name for
every record.

Multi-valued attributes:
Attributes with a set of value for a particular entity are called multi-valued
attributes. For example, some companies demands one to few phone numbers from every
customer. For such case, a record of a customer may have one or more phone
numbers.

Composite attribute is a type of attribute which represents a
value with its subparts. They can be divided in to meaningful sub parts. For example,
Address can be a composite attribute with subparts Street, City and Pincode.

22. Define null values.

In some cases a particular entity may not have an applicable value
for an attribute or if we do not know the value of an attribute for a
particular entity. In these cases null value is used.

23. Define Physical Data Independence and Logical Data
Independence.

Physical Data Independence: The power of changing the physical schema without
affecting the logical schema is called Physical Data Independence. For example,
we need not change the logical or conceptual structure of a table before
changing or upgrading the way the data stored.

Example, the different indexes used or
created on various attributes may be changed without changing the structure of
a table.

Logical Data Independence: It is about changing the logical schema without
affecting the next higher level ‘View schema’. We can alter the table structure
by adding new fields which would not affect all the application programs or
views.

24. What is meant by the degree of relationship set?

The degree of relationship type is the number of participating
entity types.

25. Define weak and strong entity sets.

Weak entity set: entity set that do not have key attribute of
their own are called weak entity sets.

Strong entity set: Entity set that has a primary key is termed a
strong entity set.

26. What does the cardinality ratio specify?

Mapping cardinalities or cardinality ratios express the number of
entities of an entity set to which another entity set can be associated.
Mapping cardinalities must be one of the following:

• One-to-one

• One-to-many

• Many-to-one

• Many-to-many

For example, a passenger can book many tickets in a railway reservation
system, a customer may have one or more accounts in a bank system, etc.

27. Explain the two types of participation constraint.

Total: The participation of an entity set E in a
relationship set R is said to be total if every entity in E participates in at least one relationship in
R.

Partial: if only some entities in E participate in
relationships in R, the participation of entity set E in relationship R is said
to be partial.

Example: Let us assume the
tables Customer, Account and Loan. The Customer table is connected to Account
through a relationship set and connected to Loan through another relationship
set. Irrespective of having account or loan, all the customers’ personal
information is stored in Customer table. Here, all the records in Account table
are connected to one or more Customer records. But, not all the records of
Customer are connected to one or more Account records. That is, Loan customers are
connected differently. Hence, the relationship between Account to Customer is Total
and Customer to Account is Partial.

28. Define the terms i) DDL ii) DML

DDL: Data base schema is specified by a set of
definitions expressed by a special language called a data definition language.
[Data definition means the creation, deletion, and modification of table structures]

DML: A data manipulation language is a language
that enables users to access or manipulate data as organized by the appropriate
data model. [Manipulation means Insertion, Deletion, and Updation/Modification
of records and values]

29. Write short notes on relational model

The relational model uses a collection of tables to represent both
data and the relationships among those data. The relational model is an example
of a record based model.

30.Define the term ‘Relation’.

Relation is a subset of a Cartesian product of list of domains.

31. Define the term ‘Domain’.

For each attribute there is a set of permitted values called the domain of
that attribute. For example, an attribute Phone permits set of Phone numbers as
values, not anything other than phone numbers.

32. What is a candidate key?

Minimal super keys are called candidate
keys. A key for which no proper subset of it is a key is called a candidate key.

33. What is a primary key?

Primary key is
chosen by the database designer as the principal means of identifying an entity
in an entity set. Primary key is one of the identified Candidate keys.

34. What is a super key?

A super key is a set of one or more attributes that collectively allows us to identify
uniquely an entity in an entity set. A super key can contain a candidate key as
a part of it.

35. Define- relational algebra.

The relational algebra is a procedural query language. It consists
of a set of operations that take one or two relation as input and produce a new
relation as output.

36. What is foreign key?

A relation schema r1 derived from an ER schema may include among
its attributes the primary key of another relation schema r2. This attribute is
called a foreign key from r1 referencing r2. In other words, it is an attribute that
refers the set of permitted values from other tables to which it is connected.

Naïve
users / New users – They are new to DBMS or even
computers and access any database through any applications by form filling. For
example, those users who have email accounts need not do anything with the
DBMSs.

Application
Programmers – They are the programmers who develop
the applications which are accessed by other users, say naïve users.

Sophisticated
users – They are interacting with the database using
query languages like SQL.

Specialized
users – They are interacting with the database through
non-conventional systems.

39. Define Procedural DML.

Procedural DML is a Data
Manipulation Language used to manipulate data in the database. For manipulating
the database, it needs the user to specify the following;

·What
data are needed?

·How
to get those needed data?

Overall, it follows a procedure.

Example: Relational Algebra

40. Define Declarative DML.

Declarative DML is Non-Procedural
DML. It requires the user to specify what data are needed. You need notprovide on how to get those data.